Shaped bodies of carbon and process for preparing same



Nov. 3, 1959 SHAPED Booms OF CARBON AND'PROCESS FOR PREPARING SAME f 0. (PETER 2,911,319

Filed- Dec. 24. 1954' Il'ompression of shaped carbon articles by impregnation with piich and subsequent coking I Known grocess Impregnaibn in Coking of binder vacuo and introduced into Cleaning subsequent pores in annular operation G'Bphit/Zatlon pressure ireaimem kiln v 1. Compression Far and pitch w of shapea carbon arfic/es by impregnafion in irifc/g [Jain and immed/fie/y fo/iowing coking in one operation 7 l Process accord/n9 zo invenfior/ Impregnat/bn with immed/Ia fe/y fol/owing coking, shaped article remainin g 'Graphitiza tion in pitch bath INVENTOR= OTTO PETER BY [ere/ W 9% M ATTORNEY phitized.

ing agent can also be effected in one operating phase in V SHAPED BODIES OF CARBON AND PROCESS FOR PREPARING SAME Otto Petr-r, Frankfurt am Main, Germany; assignor to Farbwerke lldechst Aktiengesellschaft vormals Meister I Lucius & Briin'ing,Frankfurt am Main, Germany, a corporation of Germany Application December 24, 1954, Serial No. 477,597

Claims priority, application Germany December 30, 1953 6 Claims. (Cl. 117-46) The present invention relates to shaped bodies and a .process for. preparing same.

It .is known .to..compress prebaked carbon or graphitized shaped bodies which due ture of at least 750 C. The upper heating limit may be at about 1300 C. It largely depends upon the material of the receptacle in which the bodies are heated. In addition to a considerable reduction of the pore volume and the reduced permeability for gases and liquids connected therewith, the impregnation with subsequent coking helps to increase considerably the tensile strength. The reduction of the pore volume is accompanied by an improved electrical conductivity and a raised resistance to oxidation. I

In order to reach this effect the following procedure was applied hitherto:

In the first phase of the process liquid pitch is soaked into the pores of the prebaked impregnation material by applying a vacuum. Generally the pitch is charged onto the evacuated goods to be impregnated under maintenance of the appropriate temperatures, ire. of about 150 C. to about 200 C., and the penetration of the liquid impregnating agent is accelerated by working under pressure, of, for instance, about 6-8 atmospheres. impregnation is 'well performed'the'open pores of the shaped body are filled to 96%98% with the impregnating agent. Then the'impregnation material is introduced When the v during the coking procedure according to the invention.

United States. Paw Q53 2,911,319

' Patented Nov. 3, 1959 pitch is increased with the progressively higher temperatures and fiowsout of the pores. At temperatures of more than 150 C. the pitch used for the impregnation is so highly fluid that, at the margins, it flows out of the larger pores without any expansion pressure being effective, and is soaked into the heaped up coke powder.- This powder impregnated with pitch, when being coked,"

bakes to a compact mass which can be removedfrom the shaped bodies of coal only with difiiculties. Apart from the loss of precious carbon substance the hereby. caused reduction .of .the effect intended by the impregnation of the prebaked shaped body represents a great disadvantage of the known manner of operation. In the case of thin plates and tubes as well as shaped bodies with a system of pores of a larger diameter often one half, only, of the originally soaked-in pitch is coked within the pores themselves.

I have found that shaped and prebaked carbon bodies, which may also be graphitized, can be impregnated and baked until coking of the impregnating agent is effected b'y keeping the shaped bodies immersed in pitch It is, therefore suitable to place them into a bath of liquid pitch.

When operating according to the present invention the pitch present 'in' the state of resoftening is hinderedfrom flowing out by the hydrostatic pressure of the ambient liquid pitch In this manner, especially the compression of the marginal portions is best guaranteed, this being particularly necessary for obtaining a high tensile strength.- When removing the coked residues of excess pitch which surround the shaped bodies, it has .The significant differences between'flthe process of the into an electrode baking furnace, in order to coke the a pitch penetrated into the pores. The coke formed in this baking process under reducing conditions supports the structure of the shaped body and effects an improvement of the values of the tensile strength of about 25-40% compared with non-impregnated material.

impregnation and the following coking may be repeated whereby the obtained compression is reduced with'each treatment.

baking furnace or it is, ,inaddition, subsequently gra- Coking and graphitizing of the impregnatof coke powder and subjected to a baking process of several weeks. The expected quantity of coke depositing in the pores can be ascertained by the degree of im- The' surprisingly been found that the residues break away easily and the shaped bodies do not need any additional cleaning. The pitch coke resulting therefrom represents an excellentraw material which can directly be used for the production of electrodes.

invention and the known process will become further apparent by reference to the accompanying drawing.

The following table shows, for comparison, some physical properties of carbon shaped bodies which after im 'pregnation with soft pitch (softening point according to Kriimer-Sarnow 55 C.) have been coked in compliance with the normal vac'uum pressure process once in the usual manner under coke powder and once, according to the invention, in a pitch bath.

Example 1 Six baked round carbon bodies each having a diameter of 128 mm. and a length of 300 mm. were subjected to subatmospheric pressure in a vessel and subsequ'ently covered, at 180 C., with soft pitch having a v softening point of 55 C. according to Kramer-Sarnow.

pregnation and the coking value of the used impregnating agent. It has been found outthat the actual values are always less the calculated values, i.e. that a large part of the pitch laboriously pressed into the pores is lost when the usual manner of coking is applied. This After breaking the vacuum, the system comprising carbon bodies and pitch was maintained under a gauge pressure of 8 atmospheres for one hour. After being freed from excess pitch and adhering pitch film, the carbon bodies were Weighed. Thereupon three of the bodies were subjected to coking in an annular furnace under coke powder in the usual manner (treatment A) and the remaining three were placed into a bath of liquid 7 pitch and coked (treatment B) under otherwise. equal conditions. The losses of weight in the baking operation,

, 3 I the bulk densities and the pore volumes were measured and are tabulated immediately below:

When operating without losses and based on a coking value of 60% for the pitch used, a reduction of the pore volume of 6.57% absolute is calculated for a shaped body having an initial volume of the pores of 18-20% and having been completely impregnated. As in the above example the pore volume of the bodies coked under pitch is reduced by 2.7% absolute, the yielded improvement'amounts to 40% re'lativelyconsidered.

The coking procedure according to the invention may, on the one hand, be applied when shaped carbon bodies are concerned which have been impregnated, by a special treatment, in an installation working under a vacuum and pressure. It has the advantage of depositing a greater ment of the quality of the product, as shown in Example 1.

On the otherhand, however, it is possible to combine in one process the impregnation and the coking when applying the process according to the invention. This is an especially simple solution from the technical point of view. For this purpose, prebaked shaped bodies which are not yet impregnated are placed into liquid pitch, the quantity of which is so calculated that after complete filling of the pores the impregnated material is still just covered by pitch. As the temperatures in the electrode baking furnaces rise but very slowly, the liquid pitch is given enough time to penetrate into the pores. The special advantage of this variation of the process also resides in the fact that, apart from the iron tanks for 4 port and energy, compared with the working procedure in separate stages.

The details of this manner of operating are described in the following example:

Example 2 100 legs. of prebaked shaped carbon bodies of difierent form are evacuated inan iron vessel placed in a chamber under vacuum and covered by- 60.0 kgs. of liquid soft ing numerous fissures, it is possible to loosen the im-, pregnated shaped bodies without difiiculty from the coke when the process is finished. After this treatment the shaped bodies had a weight of 106.4 kgs, which is ..equal-to an. increase of weight .of 6.4% referred to the starting weight. The yield of pitch coke amounts to v31.0

- kg's. corresponding to 51.7% of utilizable coke, referred amount of coke and effecting a corresponding improvea to the pitch introduced.

The following example refers to shaped carbon bodies having one small dimension, for instance thin-walled "tubes, rings, thin plates or rods of small diameter. In this case the known processes proved to be insufficient. According to the new process, however, impregnation and the coking, free of losses, is possible without any difficulties, as can be seen from data. in the table of the reception of the pitch material to be impregnated there- Example 3.

Example 3 Two prebaked carbon tubes having an external diameterof 40 mm., a wall thickness of 8 mm. and a length.

of 139. and 141 mm. respectively were used. As described-in the foregoing example, the first sample was impregnated in the pitch bath and coked in one phase.

The second sample was impregnated according to the .method described in Example 1 and then coked under coke powder. The greater efiiciency of the process according to the invention is to be seen in the following table giving the technological data.

before the treatment after the treatment Kind of process test material weight weight increase weight weight, per unit volume weight, per unit volume grams volume of pores gr. volume of pores gr. percent according to invent. impregnated in 1 phmz, tube of 40 mm. ext. 24 164.9 1.51 22.6 184.5 19.6 11.9 1. 72 13.5

coked under pitch without applying a vacuum mm. lint. baked 139 a mm. ong. impregnatedlnan apparatus under vacuum and tube of 40 mm. ext. 5, 21 165.4 1. 49 23.0 180. 8 16.4 9.4 1. 67 17. 1

pressure coked under a packing mass. mm. Iint. k1: baked 141 mm. ong.

with, no complicated pressure or vacuum installations are necessary. The fact that the preheating period in the annular furnace extends over a long period-about four The following Example 4 shows the application of the invention in the case of using a graphitized coal .tube

and clearly demonstrates the high efiiciency of the process days with raising of the temperature from about 100 C. when applied for graphitized bodies:

Example 4 before the treatment after the treatment Process test material weight volume weight increase weight volume welght, per 0! weight, per of grams unlt pores grams unit pores volume percent vol.

according to the invention impregnated and graphitized tube 48.6mm. 366 1.51 24.3 413.6 47.6 13.0 1.70 14.0

mired in 1 phase without applying a vacuum. o, 33!.4 mm. int. e.

mm. ong.

to about 500 C.--renders a good impregnation possible According to the invention it is especially easy to v and, furthermore, helps to save expenses for labor, transdensify embon and graphite crucibles, the prebaked cru- 'cibles being filled with liquid 'or also with cool pitch and I placed into the baking furnace.

' to larger dimensioned bodies, as shown by the Example 5.

'duced pressure and then immersing it in a bath of liquid pitch.-

3. The process defined in claim 1, wherein the impregnation and the coking are effected by immersion of the prebaked shaped body in a vessel containing pitch and placing the vessel in a baking furnace.

4. The, process defined in claim 3, including the sub-- sequent step of graphitizing the body.

Example before the treatment after the treatment Process test material weight volume weight increase weight volume welgbt, per of weight, per 01 kg. unit pores kgs. unit pores volume kgs. percent vol.

according to the invention impregnated in one round body 195 mm. 45, 12.02 1. 64 18.0 12. 75 0.73 6. 1 1. 75 12. 4

phase and coked under pitch. 45 mm. long. I

Thecomparative values tabulated inthe "following" Example 6 show the superiority of the process according to the invention also as regards the values of tensile "5."The process defined in claim 4, wherein the impregnation is eilected by charging liquid pitch under vacuum into the vessel containing the preshaped coal body.

In certain cases the filling under vacuum of the vessels charged with impregnated material maybe of advantage. In order to facilitate penetration of the impregnating agent it is suitable, in the case of cylindrical bodies, to remove, in a thin layer, the skin which is formed during the baking procedure, or,- when prismatic shaped bodies are concerned,to scratch the skin at spaced intervals in order to make it more permeable to the pitch.

' Example 7 illustrates the better eflect to be obtained by abrading the baking skin.

strength. 6. A process for treating a prebaked and shaped car- Example 6 bending strength, kg/cm.

impregnated Ln according to the the apparatus invention im- Klnd 0! test material non-treated under vacuum pregnated under sample and pressure liquid pitch and coked under coked in one coke powder phase rods 0140 x mun, 120 mm., long baked:

sample I p 193 246 263 sample II 198 251 277 bon body which comprises removing a portion of the skin formed on said body in the prebaking operation, impregnating and immersing said prebaked shaped carbon body with and in a bath of liquid pitch, baking the impregnated and still immersed body until coking of the impregnated pitch is effected, and thereafter separating the baked body from the carbonaceous matter formed from the bath of liquid pitch during the baking step.

Example 7 increase weight volume Process test material in weight per unit of pores percent volume rods of x 50 mm. baked li zgi"' According to the invention in one with baking skin. 5 test 9 phase impregnated and coked 1st test 2 i "13:5 under pitch rods of 50 x 50 mm. baked, 0nd

baking skin abraded. test 9 I clai References Cited in the file of this patent 1. A process for treating a prebaked and shaped car bon body which comprises impregnating and immersing a prebaked shaped carbon body with and in a bath of liquid pitch, baking the impregnated and still immersed body until coking of the impregnated pitch is effected, and thereafter separating the baked body from the carbona ceous matter formed from the bath of liquid pitch during the baking step.

2. A process as defined in claim 1 wherein the impregnation is effected by subjecting the carbon body to re- I UNITED STATES PATENTS 

1. A PROCESS FOR TREATING A PREBACKED AND SHAPED CARBON BODY WHICH COMPRISES IMPREGNATIG AND IMMERSING A PREBAKED SHAPED CARBON BODY WITH AND IN A BATH OF LIQUID PITCH, BAKING THE IMPREGNATED AND STILL IMMERSED BODY UNTIL COKING OF THE IMPREGNATED PITCH IS EFFECTED, AND THEREFTER SEPRATING THE BAKED BODY FROM THE CARBONACEOUS MATTER FORMED FROM THE BATH OF LIQUID PITCH DURING THE BAKING STEP. 